This invention relates to a method for the manufacture of a composite metal wire including a core metal wire having extruded therearound a coating metal layer which is different in material from the core metal wire.
Conventionally, a composite metal wire has been manufactured according to methods well known to those skilled in the art and put into a practical use for many purposes. In one of the typical methods, a composite metal wire is manufactured with use of composite billets. Such a billet has a construction of an inner core metal and an outer coating metal which are concentrically positioned. In another method, a composite metal wire is manufactured with the extrusion of a coating metal around a running core wire. In the former method wherein the composite billet is used, an extruder or a rolling apparatus has been adopted.
In such a method of manufacturing a composite metal wire, it is desirable that a composite metal wire be continuously manufactured in an infinite length and that a uniform quality is obtained along the entire length thereof.
In a method of using a composite billet, however, such a billet proves itself a limitation with regard to the volume thereof so that it is definitely impossible to manufacture a composite metal wire of an infinite length. For this reason, a predetermined number of the composite billets must be connected one after another in every stroke of the extrusion operation to provide a desired length of the composite metal wire. However, such a connection of composite billets is extremely difficult during the manufacture thereof. Accordingly, the manufacturing operation is interrupted by this connection of composite billets. This results in a lower productivity in the manufacture of a composite metal wire. Further, even if a composite metal wire of an infinite length can be manufactured in the method as set forth above, it has been considered extremely difficult to provide a composite metal wire with a uniform quality along the entire length thereof.
On the other hand, the coating metal also proves itself a limitation with regard to the volume thereof even in a method of extruding a coating metal layer on a core wire although the core wire is easily available in an infinite length. Accordingly, it is absolutely required that the coating metal be recharged into an extruder during every stroke of the extrusion operation to provide a composite metal wire with such a length. However, a lower productivity also results from the interruption of the manufacturing operation in accordance with the recharging process thereof. In this method, especially, the so-called "stop-mark" is often observed on the products as an indication of why it is difficult to uniformly control the condition of extruding a coating metal layer by different extrusion strokes.
As explained above, the disadvantages in the methods of using a composite billet and of extruding a coating metal layer are that it is impossible to continuously manufacture a composite metal wire and irregularities on the material used are found longitudinally on the products. Especially, it has been regarded as a great problem that such irregularities are produced due to the above mentioned reason during the manufacture of an electrical conducting wire such as an aluminium-clad steel wire (aluminium coated steel wire)